Method of controlling press power in a limbing knife assembly in a single-grip harvester head

ABSTRACT

In a method, when using a single-grip harvester head for felling and processing trees, of controlling the press power which, by means of a limbing knife assembly ( 6 ), is exerted on a stem ( 3 ) which is horizontally fed through th head with its butt end first, the diameter of the stem is measured and the press power is reduced in accordance with a control diagram as the diameter decreases during the feeding. The measured diameter values are registered, and each measured diameter value is compared with a predetermined diameter value which is selected from the diameter values of the stem ( 3 ) which are previously registered during the feeding of the stem. If a measured diameter value is found to equal or be greater than this predetermined diameter value, the press power is increased to a corrective power value, which is maintained until a later measured diameter value falls below a reference value.

FIELD OF THE INVENTION

[0001] The present invention relates to a method,

[0002] when using a single-grip harvester head for felling andprocessing trees, which head has a frame mounted on a forest machine anddefines an essentially horizontal tree feeding path, two rotatablefeeding rollers which are arranged on either side of said path andadapted to grip and to feed along the feeding path a stem, and at leastone limbing knife assembly which is adapted to limb a stem which in anessentially horizontal position to which it is elevated by the head isfed by the feeding rollers along said path with its butt end first, thelimbing knife assembly comprising an upper knife and two lower kniveswhich are each pivotable about an axis, being essentially parallel tosaid path, in order to press, from below, by means of a controllablepress power, the stem against a fixed support and together with theupper knife enclose the stem,

[0003] of controlling said press power,

[0004] in which method the diameter of the stem is measured during thefeeding of the stem and the press power is reduced in accordance with apredetermined control diagram as the diameter decreases during thefeeding,

[0005] the diameter of the stem being measured indirectly by measuringthe pivoting position of at least one of the two pivotable knives.

BACKGROUND ART

[0006] In a single-grip harvester head of the type described above, inwhich the pivotable limbing knives, which are hydraulically driven,press the stem against the upper limbing knife which here forms thefixed support, the press power generated by the pivotable knives must begreater, the heavier the stem. In order to control this, the diameter ofthe stem is measured continuously and the hydraulic pressure iscontrolled by means of control and computer equipment in such a mannerthat the press power increases the greater the diameter of the stem,i.e. the press power exerted on one and the same stem during its feedingis reduced as the stem is being fed. It is essential that the presspower is not made too great since an increased press power results inincreased friction between the limbing knives and the stem and, thus, inthe strain on the feeding rollers increasing as the tree feeding powerincreases. For this reason it is thus essential that the measuring ofthe diameter can be carried out in an accurate way. Accurate measuringof the diameter is essential also because the optimisation of themarking of the stem for cross-cutting calculated by the computerequipment is based exactly on the diameter of the stem. Accuratemeasuring of the diameter requires that the stem during the measuring iscorrectly placed in the nip between the limbing knives, i.e. abutsproperly against the support formed by the upper, fixed limbing knife.However, this is not always the case since the pivotable limbing knivessometimes tend to “spring” back to some extent as a result of the weightof the stem. The pivotable limbing knives can also “spring” back or beopened as a consequence of a tree, which is essentially horizontallyplaced in the single-grip harvester head, during processing being stuckin, for example, another tree or the driver of the forest machine onwhich the head is mounted not being flexible enough in his or hermanoeuvring of the head relative to the tree or the stem.

SUMMARY OF THE INVENTION

[0007] The object of the present invention is to provide a method ofcontrolling the press power generated by the pivotable limbing knives insuch a manner that the pivotable limbing knives are safely brought backto a “closed” position as soon as they “spring” back.

[0008] According to the invention, this object is achieved by a methodwhich is of the type stated by way of introduction and is characterisedin

[0009] that the diameter values which are measured by degrees during themeasuring of the diameter are registered,

[0010] that each measured diameter value is compared with apredetermined diameter value being selected from the diameter values ofthe current stem which are previously registered during the feeding ofthe stem,

[0011] that, if a measured diameter value is found to equal or begreater than this predetermined diameter value, the press power isincreased to a corrective power value which is considerably higher thanthe press power value which, according to the predetermined controldiagram, corresponds to this measured diameter value, and

[0012] that this corrective power value is maintained until a latermeasured diameter value falls below a reference value which is somewhatgreater than or equals said predetermined diameter value,

[0013] after which the press power is once again controlled inaccordance with the predetermined control diagram.

[0014] Preferably, the corrective power value equals or is greater thanthe value of the press power which, in accordance with the controldiagram, is exerted on the stem where its diameter is at its maximum.

[0015] The predetermined diameter value preferably equals the lowestregistered diameter value of the current stem.

[0016] Preferably, the reference value equals said predetermineddiameter value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention will now be described in more detail with referenceto the accompanying drawings.

[0018]FIG. 1 shows a single-grip harvester head during the processing ofa tree.

[0019]FIG. 2 shows a limbing knife assembly and circuits arranged forcontrolling the same.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0020] The single-grip harvester head 1 shown in FIG. 1 is adapted tofell and process trees and has a frame 2 by means of which the head ismounted on a forest machine (not shown). The frame 2 defines a treefeeding path, i.e. a path along which a felled tree 3 is fed through thehead 1 for processing. This path is essentially horizontal when thesingle-grip harvester head 1 is in its processing position, as shown inFIG. 1.

[0021] In addition, the single-grip harvester head 1 has two rotatablefeeding rollers 4 which are arranged on either side of the tree feedingpath and of which feeding rollers only one is visible in FIG. 1 andwhich are movable towards and away from the tree feeding path in orderto grip and feed along this path trees having varying stem diameters.

[0022] The single-grip harvester head 1 has also two limbing knifeassemblies 5 and 6 which are arranged at a distance from one anotheralong the tree feeding path. Each assembly 5 and 6 has three knives, ofwhich one is fixed and two are movable and which together enclose thestem 3.

[0023] The limbing knife assembly 6 which is shown to the right in FIG.1, i.e. located nearest to the top of the tree 3, and which has movableknives 6 a and 6 b and a fixed, upper knife 6 c is shown in more detailin FIG. 2. The movable knives 6 a and 6 b are each pivotable about anaxis 7 a and 7 b, respectively, which is parallel to the tree feedingpath, in order to press, from below, the stem 3 against the fixed knife6 c forming a fixed support, and together with the fixed knife enclosethe stem. The movable knives 6 a and 6 b are pivotable by means of onedouble-acting hydraulic cylinder assembly 8 a and 8 b each, the cylinder9 a and 9 b, respectively, of which is articulated to the frame 2 andthe piston rod 10 a and 10 b, respectively, of which is articulated tothe knife 6 a and 6 b, respectively. The movable knives 5 a and 5 b inthe limbing knife assembly 5 shown to the left in FIG. 1 are pivotablein the same way by means of one hydraulic cylinder assembly each. Themovable knives 5 a and 5 b are thus pivotable in the same manner as themovable knives 6 a and 6 b.

[0024] The limbing knife assembly 6 has a measuring means 11 formeasuring the diameter of the stem 3 which is fed through thesingle-grip harvester head 1. The measuring means 11 consists of a pulsegenerator 11 a and 11 b which is arranged on each of the two movableknives 6 a and 6 b, respectively, of the limbing knife assembly 6, andindirectly measures the diameter of the stem 3 by measuring the pivotingposition of the movable knives 6 a and 6 b.

[0025] The single-grip harvester head 1 also has a sawing device 12. Thesawing device 12 has a guide bar 13 which is connected to the frame 2for pivoting about an axis parallel to the tree feeding path. The guidebar 13 supports a saw chain 14 which is mounted thereon and which isdriven by a hydraulic motor 15 arranged on the frame 2. The guide bar 13is by means of a double-acting hydraulic cylinder assembly 16 pivotablebetween an upper starting position, in which the guide bar 13 is locatedabove the stem 3 which is to be cut off and a lower end position, inwhich the saw chain 14 has cut off the thickest stem that can beprocessed by means of the single-grip harvester head 1, i.e. a positionin which the guide bar 13 is located a distance below this stem.

[0026] In FIG. 2, P designates the outgoing conduit from a hydraulicpump (not shown) which is driven by a diesel engine (not shown) whichalso drives the forest machine on-which the single-grip harvester head 1is mounted. T designates a conduit leading to a tank 17.

[0027] The conduit P is via an electrically controlled pressureregulating valve 18 connected to an electrically controlled multipathvalve 19. The conduit T is also connected to the valve 19. One chamberof the hydraulic cylinders 8 a and 8 b is connected to the valve 19 viaa system of conduits 20, and their second chamber is connected to thevalve 19 via a system of conduits 21. The hydraulic cylinder assemblieswhich are connected to the knives 5 a and 5 b in the limbing knifeassembly 5 are connected to the systems of conduits 20 and 21 in thesame manner as the hydraulic cylinder assemblies 8 a and 8 b. A controlcomputer 22 is connected to the valves 18 and 19 in order to controlthem. The pulse generators 11 a and 11 b are connected to the controlcomputer 22.

[0028] The valve 19 can take three different positions, namely a firstposition shown in FIG. 2, in which the conduit P communicates with thesystem of conduits 20 and the conduit T communicates with the system ofconduits 21, a second position, in which the conduit P communicates withthe system of conduits 21 and the conduit T communicates with the systemof conduits 20, and a third position, in which all these connections arebroken.

[0029] When using a single-grip harvester head 1, a stem 3 is fedthrough the head by means of the feeding rollers 4. The stem 3 is fedwith its butt end first, i.e. in such a manner that its diameter in thearea of the measuring means 11 is continuously decreasing. The stem 3 ispressed against the fixed knives in the two limbing knife assemblies 5and 6 by the movable knives 5 a, 5 b and 6 a, 6 b, respectively. Thethree knives in each limbing knife assembly 5 and 6 together enclose thestem 3 in order to limb it during its feeding. The press power which isexerted on the stem 3 by the movable limbing knives 5 a, 5 b and 6 a, 6b is reduced as the stem is being fed and thus its diameter decreases.

[0030] The control computer 22, which during the feeding of the stem 3keeps the valve 19 in its first position (FIG. 2), receives themeasuring signals of the pulse generators 11 a and 11 b which signalsindicate the pivoting position of the movable knives 6 a and 6 b andcontrols, depending on these measuring signals, which are converted bythe control computer 22 to measured diameter values of the stem 3, thepressure regulating valve 18 in order to reduce the press power inaccordance with a predetermined control diagram. The diameter valueswhich are measured by degrees are registered by the control computer 22,possibly after a predetermined time delay which, for example,corresponds to the time required for transferring a point on the stem 3from the measuring means 11 to the guide bar 13.

[0031] The control computer 22 compares every measured diameter valuewith a predetermined diameter value being selected from the diametervalues of the stem 3 which are previously registered during the feedingof the stem being processed. This predetermined diameter value hereequals the lowest registered diameter value of the stem 3 beingprocessed. If the movable knives 6 a and 6 b, which are provided withthe pulse generators 11 a and 11 b, for some reason are slightly openedand, thus, do not press the stem 3 properly against the fixed knife 6 cor even risk being opened to such a degree that the stem 3 can fall tothe ground, the measuring signals generated by the pulse generatorscorrespond to a diameter value of the stem which is greater than thelowest registered diameter value of this stem 3. By controlling thepressure regulating valve 18, the control computer 22 then increases thepress power exerted by the movable knives 5 a, 5 b and 6 a, 6 b to acorrective power value which is considerably higher than the press powervalue which according to the predetermined control diagram correspondsto this measured diameter value of the stem. The corrective power valuehere equals or is greater than the value of the press power which, inaccordance with the control diagram, is exerted on the stem 3 where itsdiameter is at its maximum. The corrective power value is maintaineduntil a later measured diameter value of the same stem 3 falls below apredetermined reference value which is somewhat greater than or equalsthe predetermined diameter value. Subsequently, the press power is onceagain controlled in accordance with the control diagram.

1. A method, when using a single-grip harvester head (1) for felling andprocessing trees, which head has a frame (2) mounted on a forest machineand defines an essentially horizontal tree feeding path, two rotatablefeeding rollers (4) which are arranged on either side of said path andadapted to grip and to feed along the feeding path a stem (3), and atleast one limbing knife assembly (5, 6) which is adapted to limb a stemwhich in an essentially horizontal position to which it is elevated bythe head is fed by the feeding rollers along said path with its butt endfirst, the limbing knife assembly (5, 6) comprising an upper knife (6 c)and two lower knives (5 a, 5 b; 6 a, 6 b) which are each pivotable aboutan axis (7 a, 7 b), being essentially parallel to said path, in order topress, from below, by means of a controllable press power, the stem (3)against a fixed support and together with the upper knife (6 c) enclosethe stem, of controlling said press power, in which method the diameterof the stem (3) is measured during the feeding of the stem and the presspower is reduced in accordance with a predetermined control diagram asthe diameter decreases during the feeding, the diameter of the stembeing measured indirectly by measuring the pivoting position of at leastone of the two pivotable knives (5 a, 5 b; 6 a, 6 b), characterised inthat the diameter values which are measured by degrees during themeasuring of the diameter are registered, that each measured diametervalue is compared with a predetermined diameter value being selectedfrom the diameter values of the current stem which are previouslyregistered (3) during the feeding of the stem, that, if a measureddiameter value is found to equal or be greater than this predetermineddiameter value, the press power is increased to a corrective power valuewhich is considerably higher than the press power value which, accordingto the predetermined control diagram, corresponds to this measureddiameter value, and that this corrective power value is maintained untila later measured diameter value falls below a reference value which issomewhat greater than or equals said predetermined diameter value, afterwhich the press power is once again controlled in accordance with thepredetermined control diagram.
 2. A method as claimed in claim 1,wherein said corrective power value equals or is greater than the valueof the press power which, in accordance with the control diagram, isexerted on the stem (3) where its diameter is at its maximum.
 3. Amethod as claimed in claim 1 or 2, wherein said predetermined diametervalue equals the lowest registered diameter value of the current stem(3).
 4. A method as claimed in any one of the preceding claims, whereinsaid reference value equals said predetermined diameter value.